We describe a patient who was admitted with acute onset of dyspnea and pleuritic chest pain. The patient was in acute hypoxic respiratory failure documented by arterial blood gas levels. The severe hypoxemia was refractory to 100 percent O2 administration. The cause of the patient's sudden deterioration was a pulmonary embolus documented by angiography. The patient was managed successfully with heparin therapy. A continuous positive airway pressure (CPAP) mask corrected the severe hypoxemia, which otherwise would have required a more invasive method of respiratory support.